This horror of formlessness led to the "green belts" to mark the boundaries between town and country and prevent further attenuation of the qualities of urban - and rural - life. But once again, cities are changing and so, too, is the countryside, with radical implications as to how people will live in future. The binary opposition of urban and rural is no longer tenable or productive. But this news has not yet reached the planners or politicians.
It is likely that the settlements which will emerge in the coming decades - which may well be quite new and different versions of the inner city, town centre, suburb, edge city, waterfront, market town, urban village, tele-cottage, New Age commune - will have a greater influence on people's lives and aspirations than the global media or developments in information technology, the current front-runners in the "this is going to change the way we live for ever" stakes. Locality, increasingly, is destiny.
Social and demographic change continues to be determined more by culture than technology. There are massive processes of restructuring happening to populations in both the city and the countryside. The most important may be the overwhelming rise of single-person households, "the most pervasive trend of the Eighties", according to the Office of Population Censuses and Surveys' journal, Population Trends. It is estimated that 4 million new households will emerge in the next two decades, needed for new kinds of familial and domestic relationships, and requiring more flexible kinds of housing and tenure agreements, as well as reflecting the continuing rise of the one-parent family (Britain has the highest number of any European country). There is also the impact on the countryside of nearly a quarter of a million second homes.
All these demographic shifts are reshaping cities, towns and villages much more than the spread of personal computers or the sales of mobile phones and modems. Last week's White Paper on rural England drew attention to some of the disturbing trends in rural poverty and social displacement as long-standing rural families and their children are priced out of local housing markets by wealthier urban incomers. Some of those young people will end up joining the army of urban homeless.
The complexity of the increasing overlap between town and country patterns and lifestyles is daunting, and in urgent need of new thinking and greater public debate. A sustainable future depends on it. We have to start by asking whether the British actually like cities or, even after 200 years of intense urbanisation, have yet come to terms with urban life. There are still major contradictions in attitudes and aspirations, for while more than 80 per cent of British people live in cities, more than two- thirds would choose to live in a small town or country village if they could, according to recent research.
Some manage to escape. In 11 cities or urban boroughs - Bristol, Bromley, Cardiff, Greenwich, Hounslow, Leicester, Merton, Middlesbrough, Sheffield, Southwark and Sutton - studied recently for the Comedia/Demos Park Life report on urban parks and open spaces, all suffered depopulation between 1981 and 1991. In just one decade, Bristol dropped from 438,038 to 370,300 and Southwark from 313,413 to 196,500, although both now claim to have halted the exodus.
The flight from the cities in post-war Britain has been uneven but pronounced, and would be more noticeable but for the numbers of ethnic minority immigrants who replaced those who left. Britain's black and Asian communities overwhelmingly live in cities (and within them in quite specific concentrations or districts), and are likely to be the last groups to venture into the rural hinterland - even for a day, let alone to live. It is still the case that the countryside remains "white". Racism is, of course, one of the unspoken factors that informs some people's decisions to seek the rural idyll.
However, the usual reasons are the softer "quality of life" issues rather than housing or job prospects. People fear street crime, they worry about pollution and the health of their children, and view with increasing dismay the ageing infrastructure of services around them - pre-war schools, 19th-century hospitals, Carnegie libraries, Victorian parks fraying at the edges, privatised buses churning out diesel smoke, boarded-up department stores and shuttered high streets.
What they want are out-of-town shopping malls easily accessible by car, multi-facility "leisure boxes" built on greenfield sites, country parks with car parks and interpretation centres, and modern schools to which their children can walk in safety.
The Park Life study showed that city dwellers with cars preferred to visit a country park or out-of-town garden centre at the weekend than to walk to their local park; and the Council for the Protection of Rural England's report Leisure Landscapes, published last year, detailed the scale of the urban invasion into the countryside as a place for sport and recreation, noting that 45 per cent of all car journeys are now made for leisure purposes.
The CPRE report showed how great the pressures on the countryside are in terms of active sports and recreation, as leisure and tourism-based jobs replace agricultural jobs and leisure woodlands and golf courses take up set-aside arable land. In 1950 there were 700,000 agricultural workers; today there are 200,000. Only 6 per cent of rural workers are now employed in agriculture. The very notion of a working landscape, of rural life as a productive agricultural life, is now under siege as the Common Agricultural Policy and discretionary leisure spending combine to turn the countryside into a playground, heritage trail or site for new kinds of expensive housing estates, confirming that urban and rural problems are becoming increasingly interlocked.
As was obvious at last month's National Trust centenary conference (a watershed of public heart-searching and self-criticism), an increasing part of the Trust's work in managing its rural sites and properties is in reducing rather than increasing visitors.
As a body the National Trust is quietly powerful, not just in terms of its 2 million membership but also in its extensive ownership of land and organisational strength. It could park a lot of metaphorical tanks on other people's lawns, if it so wished, including the Government's.
It was obvious at the Manchester conference that the National Trust now has its eye on the urban heritage and a keen interest in urban issues, organising workshops in association with the Black Environmental Network and on a number of other city initiatives.
It is significant that the Countryside Commission, too, is beginning to make inroads into urban planning policy. Its offshoot, the Groundwork Trust, now largely works in urban areas on derelict land reclamation, and the commission has recently published a report on Urban Trees. Even more provocative, perhaps, was the recent launch by the CPRE of its "Urban Footprints" campaign, in favour of increased urban consolidation under the slogan: "The future of our countryside depends on our towns and cities treading more lightly on the environment."
The sub-text of this campaign could be thought to suggest, be it ever so gently, that city-dwellers should stay where they belong. Suddenly in Britain it seems that we are getting to a ridiculous situation where urban policy is being developed, by default, by rural pressure groups, some of which are keen to ensure that the urban masses stay put in their city enclaves.
Cynics might also detect a degree of opportunism in the way in which rural and landed interests are wrapping themselves in the green flag and claiming environmental reasons for keeping the countryside free of outside intruders. However, there is little that can prevent the urban rich from buying into rural life, rather than simply visiting it. The modern village or market town, certainly in the South-east, is becoming a dormitory settlement, as people work in the city but go home at night to their version of the rural idyll.
It was ever thus according to the historian Martin Weiner, whose book English Culture and the Decline of the Industrial Spirit noted how frequently the industrial masters moved to join the rural aristocracy once they had made their pile. But the urge to leave Albert Square or Coronation Street to live in Ambridge still seems a pervasive ingredient of the English dream.
The only people who claim to love cities are the families and children of immigrants who have settled here. When I recently interviewed the Guyana- born novelist Mike Phillips for a Radio 4 programme, he was effusive about the magnetism of the city: "You must understand," he told me, "we never had the myth of a rural paradise. We embraced the city because it meant progress - material progress, intellectual progress and educational progress."
The positive contribution that ethnic minority communities have made to British urban life remains largely unacknowledged.
The problem is, as Raymond Williams put it in The Country and the City, that if the countryside represents the past and the city the future, where does this leave the present? The challenge which Jonathon Porritt threw out at the National Trust conference was precisely on this issue: that the countryside has to be developed to suit modern needs. He raised the spectre of wind farms, currently a powerful symbol of rural opposition to modern life - almost wholly on aesthetic grounds. Porritt is in favour of wind farms and went on to unnerve some of the audience by arguing that in the move to develop environmentally sustainable ways of life, "landscape is not high on the list of factors which should be taken into account".
This was always Williams's argument - that landscape was the enemy of a working rural economy - and that aesthetic arguments about rural landscapes were invariably invoked to prevent any new thinking about new ways of working and living.
But new ways of working and living are precisely what Britain needs, as more and more demographic and social pressures and conflicts come to a head both in urban and rural areas. As the boundaries are breached between men's work and women's roles, between education and livelihood, between work and home, it is time to reconfigure the relations between town and country. We need planning and social policies which can provide both liveable cities and a productive, working countryside - and all the settlements and ways of life that might emerge in the spaces in between.
The author's most recent book, 'Staying Close to the River: Reflections on Travel and Politics', was published by Lawrence & Wishart earlier this year.